1. Field of the Invention
The present invention relates to a transparent film for carrying a toner image formed by an electrophotographic or electrostatic printing method. More particularly, the present invention relates to transparent films for use with an overhead projector (OHP) or a slide projector and to a method for forming a color image on this transparent film.
2. Description of the Related Art
In the prior art, the following steps are generally performed: a mono-color image is formed on a film of, for example, transparent polyester, by an electrophotographic apparatus; images obtained are used with OHP or the like and used as projection images.
In recent years, full-color images are formed by using this electrophotographic apparatus. Present demand for outputting full-color images onto a transparent film as the above-mentioned projection image has risen. However, if a transparent film, the surface of which is smooth, is used, frictional resistance will increase between various parts which are brought into contact with the transparent film in a transport passage inside the electrophotographic apparatus, and this presents a problem in that the passage will become clogged.
In the prior art, means used to solve the above-described problem are the following. A thin film formed of resin containing inorganic fine particles called a mat agent, such as silicon dioxide or alumina, or starch or the like, is formed on the surface of such a transparent film as that described above. A dynamic friction resistance is appropriately adjusted by a roughened surface formed by these particles.
The average diameter (the average particle size) of surface-roughening particles (particles of a mat agent) used on that occasion is usually 0.2 to 20 .mu.m. With surface-roughening particles of a size large enough that an adequate strongly surface roughness is achieved, the roughened surface disperses incident light, resulting in a decrease in the transparency of the transparent film. Because the amount of surface-roughening particles to be added must be increased to make the roughness uniform over the entire surface, this fact also causes a decrease in the light transmittance of a base film. As a result, problems arise in that a projected image becomes unclear, and color tone is likely to become gray on the whole when a projected image is a color image.